The main hypothesis of this proposal is that parasites play a role in preventing the development of skin prick test reaction to aeroallergens and decreases asthma severity. Helminthic infections are highly prevalent in the world and many infected people are also additionally exposed to other infections and diseases, therefore, this project proposes to evaluate whether helminthic infections down regulate the immune response of allergic diseases resulting in less severe form of asthma and absence of skin prick test response to aeroallergens. The specific aims are: 1. To determine if infections by helminthes interfere with asthma severity. To address this goal at the start of the study and every 2 months during the follow-up year, in infected and uninfected asthmatic subjects, it will be used a questionnaire to evaluate asthma severity, as well as perform a peak flow test and pulmonary function test; 2. To determine the mite fauna and mite allergen levels in house dust samples. To address this goal dust samples from patients house will be collected and evaluated to mite; 3. To both, compare the immune response of asthmatic patients infected by helminthes with uninfected asthmatic patients, and to evaluate the role of IL-10 in regulating this immune response. To address this aim we will perform PBMC culture stimulated with Dermatophagoides pteronyssinus (Der p 1) in the presence or absence of rhlL-10 and evaluate: histamine release, basophil activation and type 1 and type 2 cytokine production. A controlled study of asthma severity and the mechanism by which atopic patients, living in endemic areas of helminthic infections do not respond to the skin prick test to aeroauergens, could lead to the development of new perspectives of prevention and therapy for both asthma and helminthic infections.